Ethylene/.alpha.-olefin copolymers and ethylene/.alpha.-olefin/diene copolymers have no unsaturated bonds in their main chains, so that they show superior weathering resistance, heat resistance and ozone resistance to those of diene rubbers, and they have been broadly used for automobile industrial parts, industrial rubber parts, electrical insulating materials, civil engineering and building materials, and rubber products such as rubberized fabric. With demands of better performance and higher functions of these rubber parts and products, their shapes becomes more complicated, and therefore rubber materials having higher flowability are desired from the viewpoints of precision moldability and productivity in molding, for example, transfer molding, injection molding and cast molding.
As the rubber material, a low-molecular weight ethylene/.alpha.-olefin/diene copolymer, or a high-molecular weight ethylene/.alpha.-olefin/diene copolymer blended with a large amount of a process oil has been hitherto used.
However, the use of the low-molecular weight ethylene/.alpha.-olefin/diene copolymer may cause lowering of properties, partcicularly strength of molded products. On the other hand, use of the high-molecular weight ethylene/.alpha.-olefin/diene copolymer blended with a large amount of a process oil liable to stain a mold because of bleeding of the oil or to insufficiently vulcanize and thus to lower properties of the molded products.
Accordingly, there has been a need for foam processable rubber compositions which are capable of providing vulcanized rubber foam-molded products (sponge rubbers) having excellent vulcanization properties such as heat resistance, weathering resistance, ozone resistance and tear strength and which show excellent precision moldability and productivity in transfer molding, injection molding and cast molding, and vulcanized rubber foam-molded products of the rubber compositions.